A variety of conventional pedicle screws are known to those of ordinary skill in the art. These pedicle screws typically consist of a threaded screw portion including an enlarged head and a head body, or tulip. The threaded screw portion engages a pedicle of a vertebra of the spine, and the head body engages the head of the threaded screw portion, optionally by passing the threaded screw portion through a hole manufactured into the bottom portion of the head body until the head is seated in or adjacent to the bottom portion of the head body, for example. Other coupling configurations may also be used. The pedicle screws can be monoaxial or polyaxial, allowing the head body multiple degrees of freedom with respect to the threaded screw portion. Once placed, rods are inserted into the head bodies of adjacent pedicle screws and set screws are placed to simultaneously secure the head bodies to their respective threaded screw portions and to lock the rods in place. A rigid framework is thereby formed, suitably stabilizing and fixing the vertebrae of the spine in a predetermined alignment. Although a pedicle screw is illustrated and described herein, it will be readily apparent to those of ordinary skill in the art that the principles of the present invention apply equally to other types of bone screws and bone anchors.
When various surgical implant devices, well known to those of ordinary skill in the art, disposed in or placed adjacent to bony surfaces, it is desirable that adequate friction is present to hold them in place and that surfaces are available for bony fixation, ingrowth, and purchase over time. Accordingly, these surgical implant devices often incorporate mechanically-manufactured friction surfaces formed by conventional subtractive manufacturing processes, or utilize friction coatings or bondings for such purposes. However, these mechanically-manufactured friction surfaces, typically consisting of teeth, grooves, striations, or the like, are often not adequate and do little to promote bony fixation, ingrowth, and purchase. Similarly, these friction coatings or bondings may delaminate and fail over time.
Thus, what are still needed in the art are improved bone screws and bone anchors that incorporate essentially-integral friction surfaces that are strong and durable, and that provide adequate surface area for bony fixation, ingrowth, and purchase, while still being economical to manufacture. Improved additive and pre and post-processing manufacturing processes now make this possible.